This invention is directed to an improved IC input circuit for use in a small-sized electronic instrument, such as an electronic wristwatch and, in particular, to an IC input circuit for distinguishing between respective states of binary input signals that admits of reduced power consumption and a simplified construction.
The use of integrated circuit chips in small-sized electronic instrumentation and, in particular, electronic wristwatches, has permitted small-sized highly accurate timepieces to be developed. Such integrated circuit chips, commonly referred to as "IC's", are generally utilized in electronic timepieces to define digital circuitry for processing digital information.
Accordingly, the input circuitry for conventional IC's, utilized to effect the application of control signals thereto, must be capable of distinguishing the binary state of the control signals applied thereto. For example, correction circuits and reset circuits, of the type utilized in electronic wristwatches, are controlled by the application of binary "1" or "0" input signals thereto. In order to clearly distinguish between a high level "1" and low level "0" input signal, resistance elements have been provided in order to define a "pull-up" or "pull-down" function. When a pull-down resistor is utilized in an input circuit, if the binary state input signal is not of a sufficiently high voltage level, the input resistance will pull-down the level of the input signal, so that the input signal is seen by the IC as a low level signal. However, pull-down and pull-up resistors, utilized in an IC, provide an increase in current consumption. Although the increase in current consumption has little effect on the net current consumption of the circuit, when a signal is received, as the number of input signals applied to the IC increases, the current consumption is likewise increased. Moreover, the increase in current consumption is cumulative and, hence, accelerates the dissipation of the battery, at a less than completely satisfactory rate. This is particularly the case in electronic wristwatches that require a large number of input signals to control operations performed thereby. For example, timepieces having frequency regulation circuitry, whereby the division ratio of the divider circuit is varied by the frequency regulation circuitry, or, electronic wristwatches of the type having two quartz crystal time standards for effecting temperature compensation, have a large number of input terminals. Accordingly, an improved IC input circuit that admits of reduced power consumption and is simple in design is desired.